Control device for vacuum tubes



Aprifl 9, 11929. R. s. OHL

CONTROL DEVICE FOR VACUUM TUBES Filed Aug. 14, 1925 ii f M l-15 mlINVENTOR o 0 ATTORNEY Patented Apr. 9, 11929.

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Application filed August 14, 1925. Serial No. 50,335.

. This invention relates to control devices for vacuum tubes, andparticularly to devices for preventing excessive direct current fromflowing in the output circuits of vacuum tubes.

5 A vacuum tube consists essentially of an evacuated vessel containing athermionic cathode usually in the form of a filament which can be heatedby passing a current through 1t, an anode and a discharge controlelectrode which may take the form of a wire mesh or grid, and is usuallyplaced between the oathode and the anode. This third electrode may be ofany form,since a controlling effect on the thermionic discharge from thecathode to the anode may be obtained bypositioning any conductor withrespect to the path of the discharge so that potential variationsapplied thereto will cause variations in the thermionic emission fromthe cathode to the anode. I

When the discharge control electrode is negative, as is generally thecase, all of the electrons are drawn from the cathode to the anode, nonegoing to the control electrode. A variation in the potential that isapplied to the control electrode changes the intensity of theelectrostatic field between the cathode and the control electrode,resulting in the corresponding change in the number of electrons movingfrom the cathode to the anode. Therefore, the potential variations setup between the cathode and the control electrode cause correspondingvariations in the current flowing from the cathode to the anode.

In this invention there is connected in the input circuit of a dischargetube a blocking condenser shunted by means of a leak resistance.Incoming --oscillations make the control electrode alternately positiveand negative with respect to thecathode. During the 40 part of the cyclethat the control electrode becomes positive with respect to the cathode,electrons are attracted by the control electrode and are trappedthereupon. During the other part of the cycle the control electrodebecomes negative with respect to the cathode and no electrons areattracted by the control electrode. When the part of the incoming wavethat is positive again strikes the control electrode, more electrons areattracted by the control electrode and are again trapped on the controlelectrode. When the part of this incoming wave that is negative strikesthe control electrode no electrons will be attracted by the controlelectrode. This process continues and the control electrode builds up anegative potential. The leak resistance is so proportioned .in the inputcircuit that these negative charges on the control electrode graduallyleak back to the cathode.

But when no waves are impressed on the input circuit of such a dischargetube, then the control electrode does not impede the electronic emissionfrom the cathode to'the anode, and in such a case there is danger to thetube from the excessive heating that may occur to the anode.

It therefore an object of this invention to provide means for preventingthe electronic flow between the cathode and the anode of a dischargetube when there are no waves impressed on the input circuit thereof. Itis a further object of the invention to associate a relay with the inputcircuit of a discharge tube so that when no current flows in the inputcircuit the flow of current in the output circuit 75 will besubstantially decreased.

A good understanding of this invention ma be had from the descriptionhereinafter fol owing, when read in connection with the accompanyingdrawing showing one embodiment of the invention,

The reference character 1 "represents an electrical discharge tubehaving an anode 2, a cathode 3, and a discharge control electrode 4. Abattery 5 is connected to the cathode 3 to heat the cathode toincandescence. The reference character 6 represents a line connected toa source of current (not shown) Which supplies the input circuit of thedischarge tube '1' with current by means of a transformer 7. A variablecondenser 8 is connected across the terminals of the secondary of thetransformer 7 in order to select the particular wave train that is to-beimpressed on the input circuit of the tube. A blocking condenser 9 isconnected in the input circuit of the discharge tube and is shunted bymeans of the leak resistance 10 which is connected in seriesrelationship with thewinding of a relay 11. The plate battery 12 has itspositive terminal connected to the anode 2 of the discharge tube 1through the primary winding of the transformer 13. The armature 14 ofthe relay 11 closes and opens contact 15 to connect and disconnect, re-

spectively, the plate battery 12 in the out ut circuit of the dischargetube 1. The varia l e condenser 16 is connected across the termi- Theoutput circuit may be considered to be composed of the cathode 3, theanode 2, the primary winding of the transformerx13, the plate battery12, contact 15 and armature 14.-

The arrangement operates as follows: Currents flowing from the sourceconnected to the leads 6 are impressed on the input circuit of thedischarge tube 1 through the transformer? The condenser 8 is employedfor tuning the input circuit to any desired frequency. When directcurrent flows in the input circuit the winding of the relay 11 willbecome energized and will attract the armature-14. Contact 15 willtherefore be closed and :the plate battery 12 will be connected-imtheoutput circuit to supply space current to the anode 2. The outputcircuit of the discharge tube may be tuned to any frequency, preferablythe frequency in the input circuit of the discharge tube, or to itssecond harmonic. The current in the out put circuit of the dischargetube is then transmitted to the power output circuit 17 through thetransformer 13. 1

When no alternatin current is impressed on the input circuit 0 thedischarge tube 1 there may be an excessive current flowing in the outputcircuit of the discharge tube 1 if the plate battery remains connectedto the output circuit of the discharge tube 1. Under this condition thewinding of the relay 11 will. be deenergized and the armature 14 will bereleased. The contact 15 will be opened and the plate battery 12 will bedisconnected from the output circuit of the discharge tube 1.

While this invention has been disclosed in one particular embodimentwhich is'deemed desirable, it will be understood that it is capable ofembodiment in other and Widely varled organizations without departingfrom the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. In combination, a discharge tube having a grid, filament and plate, asource of electr'omotive force, and circuit means associated with thegrid circuit of said tube and operated by the current in the gridcircuit to connect said sourceof electromotive force to the platecircuit of said tube when incoming waves are impressed onsaidgrid'circuit and to disconnect saidusource of electromotive forcefrom the plate circuit when incoming waves are not impressed on saidgrid circuit.

2. In combination, an electrical discharge tube, input and outputcircuits for said tube, a source of potential, and a relay the windingof which is connected to said input circuit and which is operated by theflow of current in said input circuit in order to connect said source ofpotential to the plate of said output circuit when energy is beingreceived by said input circuit and to disconnect said source ofpotential from the plate of said output circuit when energy is not beingreceived by said input circuit.

'3. In combination, an amplifier of the three-electrode type, input andoutput circuits for said tube, a source of potential, and a relay thewinding of which is connected .to the input circuit of said tube inseries with itstwo input electrodes so as to connect said source ofpotential to the output circuit when direct current flows in said inputcircuit and to disconnect said source of potential from said outputcircuit when no direct current flows'in said input circuit.

4. In combination, an electron discharge tube having a cathode, an anodeand a discharge control electrode, input and output circuits for saidtube, and means in the input circuit of said tube to prevent the flow ofcurrent in the output circuit when the discharge control electrode isnot negative with respect to the cathode.

5. Tn combination, a discharge tube of the three-electrode type, aninput circuit for said tube, an output circuit for said tube, and arelay, the winding of which is connected in series relationship in saidinput circuit, the armature of said relayv closing said output circuitwhen currents are impressed on the input circuit and opening said outputcircuit when-no currents are impressed on the input circuit to preventexcessive current from flowing through said output circuit.

6. In combination, a vacuum tube having a grid, a filament and a plate,an input circuit for said tube, an output circuit forsaid tube, andmeans controlled by the flow of current in the input circuit ofsaid'tube for breaking the output circuit of said tube when the electron emission from the filament to the plate is greater than normal.

7. In combination, an electron discharge tube having a grid electrode, afilament and a plate electrode, an input circuit for said tube connectedbetween the grid electrode and the filament, an output circuit connectedbetween the plate electrode and the filament, and a relay, the windingof which is in series between said gridand filament electrodes forreventing the normal electronic emission rom the filament to the plateelectrode when substantially no current is impressed on said inputcircuit.

8. In combination, an electron discharge its ' onet? tube having acathode, an anode anti a iischarge control electrode, an input circuitfor said tube connected between the discharge control electrode and thecathode, an output name to this specification this 13th day of Aucircuitfor said tube connected between the anode and the cathode, and meansinctudledl in the input circmt for substantially decreesing the flow ofcurrent in the output circuit of said tube when no current flows in theinput circuit.

En testun gust, 1925.

ony whereof, I have are my RUSSELL S. (DHL.

